In recent years, portable wireless terminals such as mobile phone terminals have been widely used. When such a mobile phone terminal is not used, an antenna provided inside the mobile phone terminal is present in a free space away from a human body or in a bag. In a case where a user uses the mobile phone terminal to perform voice communication, the antenna is present in the vicinity of the user's head. In a case where the mobile phone terminal is used to perform data communication, the antenna is present in the vicinity of a palm of a hand. In a case where the mobile phone terminal is charged, the antenna is present in some cases in the vicinity of a battery charger. Thus, a position of the antenna is changed in accordance with a usage status, and, in a case where the position of the antenna is changed, a load of the antenna is also changed by influences of a user's head, a user's hand, a battery charger, or the like. This deteriorates a property of wireless transmission and reception of a device.
In order to solve such a problem, there is proposed a technique for suppressing deterioration of the transmission and reception property (transmission and reception sensitivity) by adjusting a load value of a matching circuit.
For example, Patent Literature 1 discloses a method for adjusting a load value of a matching circuit with use of a portable wireless device such as that shown in FIG. 9. A portable wireless device 1 of FIG. 9 includes a matching circuit 102, a controlling section 105, and a storage section 106.
In a case where a controlling section 105 starts to control the matching circuit 102, the controlling section 105 examines initial load value information, stored in the storage section 106, on the basis of a signal intensity in a frequency band of a received signal detected by a signal intensity detection section 103, and, if the initial load value information for performing impedance matching is stored in the storage section 106, the controlling section 105 controls the matching circuit 102 so that the matching circuit 102 obtains a load value corresponding to the initial load value information. On the contrary, in a case where the initial load value information for performing impedance matching is not stored in the storage section 106, the controlling section 105 evolves the initial load value information with a genetic algorithm to thereby obtain matching load value information for performing impedance matching, and controls the matching circuit 102 so that the matching circuit 102 obtains a load value corresponding to the matching load value information thus obtained.
Note that a technique for adjusting a load value of a matching circuit is disclosed in, for example, Patent Literature 2.